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(No Model.)

M. G. KELLOGG. MULTIPLE SWITGHBOARD.

No. 592,383. Patented Oct. 26,1897.

illlllttllllllluutllilltil IIIIIIIIIIIIIIIIIIIIIIIIIIIIIII 4 illllilllUNITED STATES PATENT OFFICE.

WILO G. KELLOGG, OF CHICAGO, ILLINOIS, ASSIGNOR TO THE KELLOGGSWVITCHBOARD AND SUPPLY COMPANY, OF SAME PLACE.

MULTIPLE SWITCH BOARD.

SPECIFICATION forming part of Letters Patent No. 592,383, dated October26, 1897. Application filed August 5, I890. Serial No. 361,110. (Nomodel.)

To (tZZ whom it may concern.-

Be it known that I, MILO G. KELLOGG, of Chicago, in the county of Cookand State of Illinois, temporarily residing at Stuttgart, in the Empireof Germany, have invented certain new and useful Improvements inMultiple Switchhoards for Telephone-Exchanges, of which the following isa full, clear, concise, and exact description, reference being had tothe accompanying drawings, forming a part of this specification.

Hy invention relates to a telephone-exchange system in which the linesare singlecircuit lines grounded at their outer ends and normallygrounded at the central office; and it consists in a system of testingthe lines to determine whether they are in use.

In the drawings illustrating my invention, Figures 1 and 1 representsections of two multiple switchboarcls of the exchange to which the samelines are connected. Fig. 2 shows a diagram of the boards with themainline apparatus and connections necessary to illustrate my invention.Fig. 3 shows a diagram of an operators cord system to be used inconnection with the boards. Fig. A shows an operators test system to beused at the board. Fig. 5 shows a subscribers-station apparatus.

In Fig. 2, Ais a sectional view of the switchboard shown in Fig. 1, andA is a sectional,

view of the switchboard shown in Fig. 1 each as indicated by the line ate.

I place as manyboards in the central office as are found necessary ordesirable in order to properly operate the exchange. On each board isaspring-jack or other suitable switch for each line. Each switch has acontactspring which normally connects with an in sulated contact-pieceand is adapted to receive a loop-plug and, when a plug is inserted,to'disconnect the spring from the contactpiece and connect the twocontact-pieces of the plug with the spring and said insulatedcontact-piece, respectively. The switch is also adapted to receive asingle contact switch-plug and, when a plug is inserted, to disconnectthe spring from the contact-piece and connect the spring with thecontact-piece of the plug.

In the construction of the switches as shown and as will hereinafter bedescribed I prefer to have a contact-point electrically connected withthe contact-piece and on which the spring normally bears, as there isless chance of poor connection when the spring bears on a point thanwhen it bears on a surface adapted to be broughtinto connection with theplugcontacts.

In Fig. 2, g 9 represent the springs of the different switches, h h thecontact-points on which the springs normally bear, and jj thecontact-pieces of the switches connected with the points h h. Z Zare theswitch-holes. a b are the rubber strips on which the metal parts of theswitches are mounted, as shown, and through the fronts of which are theswitchholes ZZ. The contact-pieces jj are so placed along one of thesurfaces of the plug-holes as readily to form connection with one of thecontact-pieces of the loop-plugs. The holes Z Z are adapted to receivethe switch-plugs shown in Fig. 3 and marked D D, and when a plug isinserted into a switch it raises the spring g from the contact-point h,and the spring g and the contact-piece of the plug are in contact. Theseholes are also adapted to receive the loop-plug shown in Fig. 4, andwhen a plug is inserted into a hole it raises the spring of the switchfrom the contactpoint It, and the spring 9 and the contactpiece j of theswitch are in contact with the two contact-pieces of the plug,respectively.

to and as are calling-annunciators, one for each of the lines shown.Each annunciator has a pair of contact-points normally (or when theannunciator does not indicate a call) in contact with each other, butwhich are separated by the annunciator while it indicates a call. Thetwo contact-points of a pair are markedp and q, respectively. One ofthem, q, is a spring-contact, which is pressed bythe annunciator-drop,when the drop falls, away from its corresponding contact-pointcpu Thecontact-point p is represented as an anglepiece, which passes over thespring q and is in contact with the spring when the spring is notactuated by the annunciator-drop.

B is a test-battery placed in the common ground wire or connection ofthe lines.

Two lines are shown in the drawings, one marked line No. 1 and the otherline No. 2.

' and m m are their contact-pieces.

These lines are ordinary single circuit lines grounded at their outerends and having at the subscribers stations any usual and appropriatesubscribers station apparatus. Each line passes successively through thepairs, of contacts of its switches on the several boards, passing ineach case to. the spring first. It then passes through itsline-annunciator and thepair of contact-points of the annunciator to thecommon ground wire or' bring-the contact-pieces of the. plugs intocontact with the piece 0 and secure a good con- I nection; These plugsare adapted to. be inserted into any of the switches at their board, andwhen a plug is inserted it operates the switch, as above described.Theplugsshonld be inserted so that the contact-piece m is in contactwith the spring 9. The connections of the lines might havebeen reversed,so that the lines pass first tov the contactepiece of each of theirswitches, and in that case. the

pings should be inserted in such a position that their contact-piecesform connection with the pieces j of the switches. Y is the loop.- ingunswitch for the pair of cords shown. K is the calling-key, and 'u is aclearing-out annunciz'ator. t is the operatorstelephone, and'B. isherc-aljli n-g generator or battery. The circuits arev substantially asshown.

The operation of the system in connection with the switchboards willbeapparent. to.

those skilled in the art.

Etwii]; readily be apparent thatwhen a line.

is switched: by the insertion of a plug into. its

switch the lineis disconnected from. its normat ground-wireat thecentral ofiieein which is the. test battery B1" and is connected into a1 circuitwith the pair of cords. Only one pair of cords is shown, butthe connection of such other pairs, with their accompanying apparatus,as the operator may needwill be apparent to thoseskil'led in thev art.To. each pair of cords with its plugs belong a loopingin switch, aclearing-out annunciator, and a.

test system,and they are conveniently mounted and arranged for her work.

In the subscribers-station apparatus shown in Fig. 5, 1 is thetelephone-switch. 2 is the calling-generator. 3 is the signal-receiving5 hell. 4 is, the subscribers telephone. 5 is the tion-coil. 7 is thetransmitter. 8 is the transmitter-battery. 9 is a resistance-coil ofsuit- 5 able resistance to operate, as hereinafter described. Theseparts may be of usual forms of apparatus and are connected as shown orinother Ways so as to perform practically the operations required andthe operations hereinafter described.

When the subscribers telephone is on its switch, the signal-receivingbell is in the cirondary of the induction-coil, and the resistance-coilare shunted by a wire of small resistance, so as to be practically out.of the i circuit. When the telephone is 01f theswitch, the telephone,the secondary of the induction-coil, and the resistance-coil are in thecircuit and the signal-bell'is practically out g of the circuit. Theresistance of the telephone and secondary of the induction-coil combinedaggregate in well-constructed ap- Iparatus about four hundred ohms andthe resistance of the signal-bell amounts to about one-hundred ohms. Theresistance switched I into the circuit when the telephone is off itsswitch for use is therefore much greater than is the resistance in thecircuit when the telephoneis in its norm-a1 position on the switch. Iutilize this. dift'erence in resistance in the after appear. If thediiierence in the resistance when the telephone is off its switch foruse. and when it is in its normal position on the. switch is notsuificient to secure an easy adjustment of the test apparatus to thecircuits, such additional resistance as is required may be placedin theresistance-coil 9. Whether this artificial resistance is used and itsamount, if used, will depend on the apparatus and circuts to which thesystem may be applied.

The test receiving instruments and testbatteries should be soconstructed and adjusted to each other and the circuits. that 3 theinstrument will sound or respond when 1 it and the battery are loopedinto the closed circuitofany single line and. the subscribers telephoneis not off its switch for use, but will not respond if the circuit isopen at any point, or if the'subscribers telephone is off its switch andthe additional resistanccat the subscribers stationis included in thecircuit, or the line is switched with another line and thereby has itstest-circuit open, as will hereinafter be indicated. This adjustment canbe regulated as. required by the addition of artificial resistances inthe circuits. Thisconstruction and adjustment depend on the fact that anelectromaguet may be readoperation of the test system, as will hereinsecondary, and 6 is the primary, of the induc cuit of the line, and thetelephone, the sec- 'ing.

ily made so as to operate when a battery and a certain resistance is incircuit with it and not to operate when the resistance is considerablylarger. This operation can be obtained in different ways, dependent onthe style of the electromagnet, the number of convolutions of its coil,the size of the battery, and the adjustment of the retractile spring.These parts should be such that the electromagnet will be actuated whenthe test system is looped into the normal circuit of any line of theexchange, but will not be actuated when the additional resistance isintroduced. The resistance of the coils may be such as is necessary ordesirable in order to obtain such an adjustment of the parts of theexchange system.

The operation of the test system is as follows: \Vhen an operatordesires to test a line, she places her test-plug into the switch of theline and by so doing disconnects the points 9 and h of the switch andconnects them with the contact-pieces'of the plug. If, then, the line isnot switched at any board and the annunciator does not indicate a calland the subscribers telephone is on its switch, the test receivinginstrument will sound or respond, indicating that the line is free to beswitched to. If, however, the line not being switched the subscriber hassent in a call and the annunciator indicates the call or has taken histelephone from the switch for use, the instrument will not sound, as theline being open at the annunciatorpoints or the additional resistance inthe circuit will prevent it from doing so. If, again, the line isswitched at some board and the test is made in the cut-01f portion ofthe line that is, that portion which is between the switch used forswitching and the oifice ground-the instrument will not sound, becausethe test-eircuit is open at the pair of contact-points of the switchused for switch- If, again, the line is switched at any board withanother line and the test is made in some switch between the one usedfor switching and the subscribers station, the instrument will not soundon account of the battery being cut off from the circuit in which thetest receiving instrument is included.

WVhen a test of a line is made and the test receiving instrument sounds,the operator knows that neither the line is switched for use nor theline-annunciator indicates a call, and

- when the instrument does not sound she answer frequently receivesseveral calls at practically the same moment, and it may require sometime before she can switch to a certain line and answer its call.

In systems in which the test depends only on the line being switched atsome board another operator may in the meantime test the line andfinding it'to test free may switch it with another line and causeannoyance and confusion to the subscriber. I This cannot occur in thissystem of testing, because as soon as the subscriber takes his telephonefrom its switch the line will test busy whether or not it is switched atthe central office. Again, in systems of testing which depend only onthe subscribers telephone being on or off its switch confusionfrequently arises from the fact that a subscriber places his telephoneon its switch when he is through conversation without sending in aclearing-out signal and his line tests free and is connected to when itis already switched with another line. Lines in this condition aretechnically called tied up. This, again, cannot occur in this sys' tern,because the line will test busy until it is disconnected at the centraloffice whether or not the subscribers telephone is on its switch. Thesystem therefore combines the advantages and obviates the disadvantagesof the two general systems of testing outlined above. Moreover, in thissystem the line tests busy as soon as the calling-generator operates andthe annunciator indicates a call whether the subscriber may have takendown his telephone for use or have replaced it on its switch.

I claim as myinvention and desire to secure by Letters Patent- 1. In atelephone-exchange system, a tele phone-line normally on closed circuitand con taining a test-battery in its circuit, in co1nbisuch normallyclosed circuit, said instrument 1 being constructed and adjusted tosound or.

respond when looped into'such circuit and neither the telephone isswitched for use nor the annunciator indicates a call and not to respondwhen either the telephone isswitched or the annunciator indicates acall, substantially as set forth.

2. In a telephone-exchange system, telephone-lines normally on closedcircuit and each having a testbattery in circuit, in combination with anannunciator normally in the circuit of each line, with contact-points bywhich the line-circuit is open when the annunciator indicates a call, asubscribers-station apparatus for each line, containing a telephone, atelephoneswitch, resistance, contacts and connections by which a greaterresistance is Switched into the circuit of the line when the telephone,is, switched for use, a test receiving instrument and switch apparatusfor looping the same into the normally closed circuit, of either line,said instrument being constructed and adjusted to sound when loopedinto. the circuit and neither the subscribers telephone is switched northe annunciator indicates; a call and not to sound when either thetelephone is switched or the annunciator indicates a call,substansistance, contacts and connections by which a greater resistanceis switched into the circuit of the line when the telephone is switchedfor use than when it is: not thus switched, a test receiving instrumentand switch apparatus for looping the same into the normally closedcircuit of any of the lines, said instrument being constructed to soundor respondwhen looped into the circuit and neither the telephone isswitched foruse nor the annunciator indicates a call and not to respondwhen either the, telephone is thus switched or the annunciator indicatesa call, substantially as set forth. r

4. In a telephoneexchange system, a telephone-line normally on closedcircuit, in combination with an annunciator normally in the circuit ofthe line, having contact-points by which the circuit is open when theannunciator indicates a call, the subscribers-station apparatus,containing a telephone, a telephone-switch, resistance, contacts andcircuitsby which a greater resistance is switched into the circuit whilethe, telephone is switched for use than while it is not thus switched,

a test receiving-instrument, switch apparatus for looping the same intothe line-circuit and a test-battery in the circuit thereby established,said instrument being constructed to respond or sound when looped intothe circuit of the line and the annunciator does not,

- indicate a call or the subscribers telephone is not switched for useand not to sound or switch having a pair of contact-points norwhen theplug is inserted to have the contactpoints separated and connection madebetween them and the two contact-pieces of the plug, respectively, eachline passing successively through the pairs of contact-points of itsswitches, passing in each case to the line contact-point first, andthence to ground, in combination with an annunciator normally in thecircuit of eachline, each annunciator having a pair of contact-points bywhich its linecircuit is open while it indicates a call, a testbatterynormally in closed circuit with each line, a su-bscribers-stationapparatus for each line, containing a telephone, a telephoneswitch,resistance, contacts and connections by which greater resistance isincluded in the line-circuit while the telephone is switched for usethan while it is not thus switched, and a test receivinginstrument ateach board, included in a loop which terminates in the twocontact-piecesof a test-plug, each instrument being constructed and adjusted to soundor respond when it, is included in the closed circuit of either line andneither the subscribers telephone is switched for use nor theline-annunciator indicates a call and not to sound when either thetelephone is thus switched or the annunciator thus indicates,

' substantially as set forth.

6. In a telephoneexchange system, tele- 1 phone-lines grounded at theirouter ends and multiple switchboards for the same, each board containinga switch for each line, each switch having a pair of contact-pointsnormally in contact, adapted to receive a switchplug and, when the plugis inserted to have I the contact-points separated and the contactpieceof the plug in contact with the line contact-point of the switch andwith that only,

and adapted to receive a loop test-plug and its switches, passing ineach case to the linecontact-point first and from the last switch to thecommon ground of the lines in which is a test-battery, in combinationwith an annunciator having a pair of contact-points by which itsline-circuit is open while it indicates a call, a subscribers-stationapparatus for each line, containing atelephone, a telephoneswitch,resistance, contacts and connections by which a greater resistance isincluded in- 1 the circuit of the line while the telephone is ,switchedfor use than while it; is not thus 1 switched, and a test receivinginstrument at I nunciator in the circuit of each line, each aneachboard, included in a loop which termiswitched or the annunciator thusindicates,

nates in the two contact-pieces of a test-plug, substantially as setforth. 10 each instrument being constructed and ad- In Witness whereof Ihereunto subscribe my justed to sound or respond when it is includedname this 2361 day of June, 1890.

in the closed circuit of either line and neither MILO G. KELLOGG.

the subscribers telephone is switched for use Witnesses:

nor the annunciator indicates a call and not EMIL ABENHEIM,

to sound when either the telephone is thus ABBOTT L. MILLS.

